A compact is a polycrystalline mass of abrasive particles (e.g., diamond and cubic boron nitride) bonded together to form an integral, tough, coherent, high-strength mass. Representative U.S. patents on the subject of diamond compacts are U.S. Pat. Nos. 3,136,615 (boron carbide bonding medium); 3,141,746; 3,239,321 (graphite-free diamond compact); 3,744,982 (boron alloyed diamond compact process); 3,816,085; and 3,913,280. A composite compact is a compact bonded to a substrate material, such as cemented tungsten carbide (see U.S. Pat. No. 3,745,623). Representative U.S. patents on the subject of cubic boron nitride (CBN) compacts are: U.S. Pat. Nos. 3,233,988; 3,743,489 (aluminum alloy catalyst); 3,767,371 (composite) and 3,852,078 (uniform compacts are of polycrystalline CBN with other hard materials, e.g., diamond). Compacts may be used as blanks for cutting tools, dressing tools, and wear parts.
Compacts comprised of diamond, CBN, or combinations thereof bonded together with silicon and silicon carbide (silicon and silicon carbide bonded compacts) are described in U.S. Patent application Ser. No. 954,289, filed Oct. 24, 1978, which is incorporated herein by reference. They are made by infiltrating a mixture of carbon coated abrasive (e.g., diamond) and a carbonaceous material with fluid silicon under partial vacuum. This operation can be performed in a graphite mold at temperatures over 1400.degree. C.
U.S. Pat. Nos. 3,831,428; 4,129,052 and 4,144,739 disclose wire drawing dies made from diamond or CBN. Cutting tools made with compacts disclosed in U.S. Pat. No. 3,850,053. Wire drawing dies of single crystals of diamond commonly fail by cleavage. Single crystal diamond tools most commonly fail by gross fracture. Single crystal diamond can be polished to a higher degree than polycrystalline diamond tools, however, and hence give a better finish on the workpiece.
Various high pressure-high temperature (HP/HT) apparatus have been designed for the synthesis of CBN and diamond and for research purposes. The ultimate pressure capability of a high pressure apparatus is dependent on the strength of materials, the geometry, the stress distribution and the stress support available. For example, a simple piston and cylinder apparatus is limited to an ultimate pressure of about fifty kilobars (Kbar) when the piston is cemented tungsten carbide. If the piston is tapered, such as in a Bridgman anvil, the strength is increased, by geometry effects, and a pressure of 100 Kbar or more can be achieved with the same material. If the Bridgman anvil is supported and/or pressure staged such as in a Drickamer or a Kendall apparatus, pressures of 300 Kbar can be reached.
The following references go into more detail on high pressure apparatus:
Spain, I. L., High Pressure Technology, Volume 1, Chapter 11, Marcel Dekker, Inc., New York, 1977.
U.S. Pat. No. 3,191,231 (refractory nib on a punch).
U.S. Pat. No. 3,079,505 (natural diamond anvils).
Vereshchagin, L. F., Yakovlev, et al., "Dielectric-to-Metal Transitions Under Pressures P.about.1Mb", Proceedings of the Fourth International Conference on High Pressure, Kyoto, Japan, 1974, Published by The Physico-Chemical Society of Japan, Kyoto (1975).
Block & Piemarini, Physics Today, September 1976.
Bundy, F. P., "Research at Very High Pressures and High Temperatures", The Physics Teacher, pp. 461-470 (November 1977).
U.S. Pat. No. 2,941,248.
Bundy, F. P., Review of Scientific Instruments, Vol. 46, No. 10, p. 1318 et. seq., (October 1975).
The term anvil will be used to refer to the analogous pressure producing members (punches, anvils, pistons) of the various high pressure apparatus discussed herein.
Bundy achieved pressures of more than 300 Kbar by replacing cemented carbide with sintered polycrystalline diamond, thereby reaching 500 or 600 Kbar in the Drickamer design. The Soviets (Vereshchagin) claim to have reached 1000 Kbar or more using polycrystalline diamond in a simple Bridgman anvil device.
The Spain reference mentions the Van Valkenburg apparatus in which samples were squeezed between two high quality single crystals of diamond. With modifications of Block and others, pressures up to 1000 Kbar have been claimed.
At a conference, June 2-4, 1976, on high pressure phenomena at Rensselaerville, New York, the importance of the diamond anvil cell (e.g., Van Valkenburg), in research at ultra-high pressures was discussed. The optical transparency of such devices permits laser heating in the reaction zone or cell, as well as precise optical observations and spectroscopic studies.
There are limitations, however, in all this prior work in that:
1. Large diamond crystals are rare, expensive, variable in quality, generally have residual stress, and have weak plains of cleavage;
2. Bundy had only a relatively thin layer of diamond, hence the cemented carbide back-up layer was the weakest element; and
3. No means for an optical path could be made through the Bundy, Kendall or the Russian designs.
Laser systems with diamond optical elements are described in U.S. Pat. No. 3,895,313.